In a conventional image capture device such as a camera, the quantity of light to be transmitted through an optical system and incident on an image sensor is generally adjusted with an optical diaphragm or a shutter.
However, to reduce the quantity of light with an optical diaphragm, the aperture size of the optical diaphragm needs to be decreased, and therefore, a diffraction phenomenon of the light will cause a decrease in resolution, which is a problem. In addition, the aperture size of the optical diaphragm also affects the depth of field, and the shutter speed affects how the subject gets blurred if either the subject or the image capture device itself is moving. That is why according to an exposure control method that uses the optical diaphragm or the shutter speed, the resultant depth of field or way of subject's motion blur may become an unintentional one, which is also a problem.
To overcome these problems, according to a known method, the quantity of light is regulated by rotating two polarizers, which are arranged coaxially, relative to each other on their axes. According to such a method, since at least one polarizer is always present on the optical path and since some polarization components are always cut, the maximum quantity of light transmitted decreases compared to a situation where no polarizers are provided at all.
Thus, Patent Document No. 1 discloses an exposure controller which includes two polarizers and two driving sources, which regulates the quantity of light by getting the two polarizers rotated relative to each other by one of the two driving sources, and which retracts the two polarizers from the optical path using the other driving source.
On the other hand, Patent Document No. 2 discloses an exposure controller which includes two polarizers and one driving source and which not only regulates the quantity of light by getting the two polarizers rotated relative to each other, but also retracts the two polarizers from the optical path, by using the same driving source. FIG. 14 illustrates a conventional exposure controller 1000 as disclosed in Patent Document No. 2. Specifically, FIG. 14(a) illustrates a situation where the two polarizers are inserted into the optical path, while FIG. 14(b) illustrates a situation where the two polarizers are retracted from the optical path. In the conventional exposure controller 1000, the two polarizers 1001 and 1002 are fixed on a polarizer driving plate 1003 and the polarizer driving plate 1003 is moved when the polarizers 1001 and 1002 need to be retracted.
According to any of these configurations, a state where no polarizers are present on the optical path can be created, and therefore, the maximum value of the adjustable transmittance can be increased.